Hello and welcome to HCM, I read your query and understood your concern. While there has been speculations about diabetes and mysterious bruising, there is no evidence of diabetes as a cause of unexplained bruising except in long standing cases, which a young person would not be. Since all the blood work had come normal it rules out blood defects like hemophilia. Sometimes people with eating disorder suffer from nutritional deficiencies, which may sometimes cause unexplained bruises. Supplement her diet with vitamin C, B complex, vitamin K and minerals. I hope it helped.